Such notice shall be sufficient if, on or before such third day, such notice is served in the manner provided in section
7603 (relating to service of summons) upon the person entitled to notice, or is mailed by certified or registered mail to the last known address of such person, or, in the absence of a last known address, is left with the person summoned. If such notice is mailed, it shall be sufficient if mailed to the last known address of the person entitled to notice or, in the case of notice to the Secretary under section 6903 of the existence of a fiduciary relationship, to the last known address of the fiduciary of such person, even if such person or fiduciary is then deceased, under a legal disability, or no longer in existence.